[Chris Barnett]

Well, to answer my own question I found this link…

https://discussions.apple.com/message.jspa?messageID=7402247

explains that an FCP project file can become corrupt while you are working on it… at the point of corruption everything from then on is not saved, even though the project seems to be working fine and all your saves appear to be working. The problem only shows itself when you re-boot FCP.

I would still be interested to hear if anyone has had this problem and found a way to recover the corrupted work. Or has any ideas why it might have become corrupt and how to avoid this?

1 worry is that the project file which deleted my sequence, still contains other sequences, so are they also at risk? I will export each one as an XML file just in case. Any other safety tips from anyone else???

there are some good tips in the link above.